The invention relates to a process and an apparatus for cooling and atomizing liquid or pasty substances.
Cooling processes are used to change the product properties of substances. The substances to be cooled are generally treated in apparatuses whose cooling action is based on heat-transfer processes between a coolant and the substance to be cooled at cooling surfaces. The heat or cold transport between coolant and the substance to be cooled is therefore only indirect. A relatively rapid cooling of the substances, which is frequently required, cannot be achieved by this means. These cooling processes are also frequently unsuitable for carrying out a crystallization or a freezing, since insulating deposits form on the cooling surfaces which can impair the cooling process. Cooling processes of this type are, for example, described in Rompp Chemielexikon [Chemistry lexicon] and Pahlmann, Taschenbuch der Kaltetechnik [Refrigeration manual].
It is further known that on an industrial level, spraying towers are used to produce pulverulent products with the use of conventional refrigeration.
Cryogenic cooling and freezing processes in which low-temperature gases are used are also prior art. Rompp Chemielexikon and Pahlmann, Taschenbuch der Kaltetechnik, for example, disclose processes in which the substances to be cooled are sprayed with the refrigerant, in particular with liquid nitrogen or with solid carbon dioxide in the form of dry ice or snow. The direct contact of the refrigerant with the substances leads to a substantially more rapid cooling of the substances than with the abovementioned conventional processes. For a relatively rapid cooling of liquid or pasty substances this process also is unsuitable, since the cooling in the interior of the substances is determined by the heat transport through the substance itself, and the contact surfaces for a rapid cooling, for example for crystallization, are still too small. It is virtually impossible with these processes to produce readily meterable flowable substances.
The Cryopel.RTM. process, described in U.S. Pat. No. 4,967,571, the Cryobreak.RTM. process, described in DE 44 19 010 C1 and the Cryofals.RTM. process, described in DE 43 29 110 C1, are known processes in which liquid substances are cooled very rapidly by being introduced dropwise into liquid nitrogen. This cooling process can lead to a meterable pelleted substance. The particle sizes which are established are generally in the range of a few millimeters. The cooling is always performed to the temperature of the liquid nitrogen of approximately 77 K, which is not necessary or even undesirable in a multiplicity of applications.
In addition, an apparatus is known in which a liquid substance is brought into contact with liquid nitrogen, with the use of two-jet nozzles, in order to cool the substance rapidly. There is the disadvantage here that the product can be cooled as early as in the nozzle by the low-temperature nitrogen and can block this nozzle.